Decolorization of lubricating oils



DECOLORIZATION F LUBRICATING OILS William E. Thompson, Wallingford, and Robert W. Shinn,

Swarthmore, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application January 25, 1957 Serial No. 636,251

3 Claims. (Cl. 25250) This invention relates to a process for decolorizing lubricating oils, and more particularly to a process for decolorizing oils by exposure to visible light.

Hydrocarbon lubricating oils, particularly naphthenic oils prepared by distillation of essentially wax-free crude oils, contain small amounts of complex compounds which impart a dark color to the oil. While the presence of these compounds does not adversely affect the lubricating qualities of the oil, such oils are difiicult to sell because customers prefer light-colored oils.

We have now discovered that stable, light-colored oils may be produced by exposing the oil to visible light at a temperature below about 40 F., followed by'the incorporation of an antioxidant in the oil prior to bringing the oil to ambient temperatures. Exposure to visible light at room temperature has apparently no etfect on the color of the oil, and ultraviolet light, even at low temperatures, also has no beneficial eifect. The reason why light is effective at low temperatures, but not at room temperature is unknown to us, but it is speculated that at the higher temperatures, oxidation of oil components to dark colored compounds proceeds at a rate equal to the rate of removal of other colored compounds by light, so that there is no effect. The compounds destroyed by light are apparently natural oxidation inhibitors, since it has been observed that when irradiated oils are brought to room temperature without further treatment they tend to darken rapidly, and they cannot thereafter be lightened in color by further irradiation at reduced temperatures. If, however, an antioxidant such as phenylene diamine, ditertiarybutyl paracresol, or any other petroleum anti-oxidant known to the art is added to the oil in the amount of from about .0005 to .005% before bringing it to room temperature the oil will re- -main stable in storage. r

In order that those skilled in the art may more fully appreciate the nature of our invention and the method of carrying it out, the following examples are given.

Example I A quart bottle of a naphthenic lubricating oil having an O. D. color of 24.2 was placed on the laboratory roof during December, when the average temperature was under 40 F., and was below freezing most of the time. After 5 days exposure, the color had been reduced to 15.9. The sample was then taken into ther 2 once started, was autocatalytic, so that further exposure to hght did not eifect any decolorization.

Example [I A duplicate sample was placed on the roof at the same time as the first sample and was left there, without warming, for 12 days, after which time it was found that it had dropped from its original 0. D. color of 24.2 to an O. D. color of 13.5. Addition of 0.002% of ditertiarybutyl paracresol to this oil,-before warming to room temperature, produced a stable oil which did not discolor in storage.

Example III Example IV A fourth duplicate sample bottle was wrapped in tin foil so as to exclude light therefrom and was placed on the roof with the samples of the preceding examples. After 8 days it was found that the color had increased to 24.9 from the original 24.2, indicating that cold alone was ineffective to decolorize the oil.

Example V A fifth duplicate sample was irradiated by ultraviolet light for six hours at 20 F. This treatment increased the O. D. color from 24.2 to 25.9, indicating that light in the visible spectrum was responsible for the decrease in color noted in the first three examples.

Example VI A quart bottle of a lubricating oil having an initial 0. D. color of 20.1 was placed on the roof and exposed for days during the winter. It had a final color of 10.6, and could be stabilized at this color by the addition of 0.002% of phenylene diamine. A similar bottle placed in sunlight on the laboratory window sill during the same period of time was reduced in color'only from 20.1 to 19.8, indicating that irradiation by light at room temperature is inefiective in reducing color.

Example VII A quart bottle of a different lubricating oil having an initial 0. D. color of 18.4 was placed on the roof in December and kept there for six days, after which the color was found to be 12.4. A duplicate bottle kept on the laboratory shelf increased in color during the same period to 21.0.

Example VIII A quart bottle of a still different lubricating oil having an initial 0. D. color of 13.8 was placed on the roof at the same time as the bottle of Example VII. After six days, the color of this oil had decreased to 10.4 while a duplicate kept on the laboratory shelf retained its original color over the same period of time.

We claim:

1. A process for decolorizing lubricating oils which comprises bringing a petroleum lubricating oil prepared by distillation of an essentially wax-free naphthenic crude oil and containing naturally occurring impurities in an temperaturelessthan' about 40' F.', irradiatingthe'oil with light in the visible spectrum for a period of time sufiicient to eifect a reduction in the O. D. color of the oil, and adding from about 0.0005% to about 0.005% of an antioxidant selected from the group consisting of phenylene diamine and ditertiarybutyl paracresol prior to warming the oil to above about 40 F.

2. The process accordingfto claim 1 in which the antioxidant is-phenylenediamineh 3'. The process accordinglot claim:1 in which the antioxidant is di'tertiarybutyl paracresol.

References Cited in the file of this patent UNITED STATES PATENTS Lubrication Engineerin OTHER REFERENCES g, December 1950, pages 263- 

1. A PROCESS FOR DECOLORIZING LUBRICATING OILS WHICH COMPRISES BRINGING A PETROLEUM LUBRICATING OIL PREPARED BY DISTILLATION OF AN ESSENTIALLY WAX-FREE NAPHTHENIC CRUDE OIL AND CONTAINING NATURALLY OCCURRING IMPURITIES IN AN AMOUNT SUFFICIENT TO IMPART A DARK COLOR TO THE OIL TO A TEMPERATURE LESS THAN ABOUT 40*F., IRRADITING THE OIL WITH LIGHT IN THE VISIBLE SEPECTRUM FOR A PERIOD OF TIME SUFFICIENT TO EFFECT A REDUCTION IN THE O. D. COLOR OF THE OIL, AND ADDING FROM ABOUT 0.0005% TO ABOUT 0.005% OF AN ANTIOXIDANT SELECTED FROM THE GROUP CONSISTINF OF PHENYLENE DIAMINE AND DITERTIARYBUTYL PARACRESOL PRIOR TO WARMING THE OIL TO ABOVE ABOUT 40*F. 